This laboratory has been working toward characterizing the possible receptor mechanisms responsible for the therapeutic and side effects of the estrogens in oral contraceptives. The current main effort is describing the probable estrogen receptor in the mammalian liver. An interaction of the estrogen with its receptor in liver might contribute to side effects of women taking estrogens. The liver interaction may contribute to side effects by changing plasma protein synthesis (e.g., thrombosis by increasing blood clotting factors and decreasing a clotting inhibitor, anti-thrombin III), and by parenchymal changes in liver function (e.g., Benign hepatomas and cholesterol gallstones). The studies have been directed toward eventually designing or selecting safer yet effective estrogens that can be used in combination with a progestin as improved contraceptives.